Fabric adhesives are often used on fusible interlinings, which are materials such as fabric which have been coated on one side with a discontinuous pattern of adhesive. When the interlining is bonded to a face fabric in a garment, it provides body and shape to the garment without impairing the ability of the fabric to breathe. Fusible interlinings are used in the manufacture of suits, in shirt collars and cuffs, and in the waistbands of trousers. In the manufacture of suits, polycarbonate basting threads are frequently used to temporarily hold the parts of the suit in place. After the suit is completed, a solvent such as perchloroethylene or trichloroethylene is used to embrittle the polycarbonate thread so that it may be brushed from the fabric.
Binder fibers or polyester powders are frequently used to bond nonwovens, which are formed from matrix fibers into a web, sheet, or mat. The binder fibers or binder powders give strength to the web, mat, or sheet by bonding it together.
Certain polyesters are known to be useful for fusible interlining adhesives and binder fibers. For example, one polyester of interest is the copolyester of terephthalic acid, adipic acid, ethylene glycol and 1,4-butanediol as described in U.S. Pat. No. 3,699,921. Such polyesters tend to block in pellet form and fumed silica must be added in significant amounts to make it possible to grind this polymer into powder. Excessive amounts of fumed silica in the powder, however, prevent good coatability and good fusion of the powders on the fusible interlining fabric when applied with powder point applicators.
Copolyesters generally have lower melting points than homopolyesters. For example, the melting point of a polyester of terephthalic acid and ethylene glycol is around 260.degree. C. A polyester consisting of 90 mole % of terephthalic acid and 10 mole % of isophthalic acid in which ethylene glycol has been used as the diol component, has a melting point of 236.degree. C. When the molar ratio of terephthalic acid to isophthalic acid is 80:20, a copolyester is obtained which has a melting point of 210.degree. C. When the ratio of terephthalic acid to isophthalic acid is 70:30 the melting point drops to 185.degree. C.
Conditions are similar when ethylene glycol is replaced by 1,4-butanediol. A polybutylene terephthalate comparable to polyethylene terephthalate has a melting point of 225.degree. C.
In German Offenlegungsschrift No. 1,920,432 there is disclosed a dry-cleaning fluid resistant polyester fusion adhesive prepared from terephthalic acid, adipic acid, ethylene glycol, and 1,4-butanediol. The degree of crystallization of this copolyester, however, is already so low that it is not suitable for a fusion adhesive. Disadvantages reside in both the surface stickiness of the coated substrate and the stickiness of the copolyesters which is considerable even at room temperature. Copolyesters of this type are not suitable for the preparation of adhesives in powder form.
U.S. Pat. No. 4,252,940 discloses copolyester adhesives of terephthalic acid together with isophthalic, succinic, adipic or glutaric, and a blend of 1,6-hexanediol and diethylene glycol.
It is well known in the art that the crystallinity of a polyester is one parameter which may be used to determine solvent resistance, i.e., the more amorphous (less crystalline), the more susceptible to drycleaning solvents the polyester will be. Also, glass transition temperature is a parameter by which the temperature at which a polyester, even an amorphous polyester, will be affected by a solvent.
It is also known that modification of a homopolyester by copolymerization with other acid or glycol moieties or combinations of glycol and acid moieties to form copolymers or terpolymers drastically reduces or eliminates crystallinity. The crystallinity of copolyesters is also dependent on the particular comonomers from which the copolyester is synthesized. For example, a polyester of terephthalic acid and 1,4-buanediol (even number of carbon atoms) will crystallize more readily than a polyester prepared from terephthalic acid and either 1,3-propanediol (odd number carbon atoms) or 1,5-pentanediol (odd number of carbon atoms). The crystallization phenomenon of copolyesters, especially those that are low melting, below 150.degree. C., is unpredictable.
Amorphous polyesters generally cannot be used as fusion adhesives in which resistance to dry-cleaning agents and high set-up speed are required. In like manner, those polyesters are undesirable which have too little crystallinity, because they solidify too slowly and consequently do not lose their surface stickiness for long periods of time.
Other copolyesters of interest are those disclosed in U.S. Pat. Nos. 4,094,721; 3,948,859; 4,012,363; and 3,853,665.
Certain low melting, crystallizable polyesters are useful for bonding fabrics at temperatures (120.degree.-150.degree. C.) which do not damage the fabrics. These bonds generally show excellent resistance to laundering and dry cleaning treatments. Thus, these materials are useful in film, fusible interlining, or melt blown web form to laminate fabrics in the construction of wearing apparel. However, in certain industrial lamination applications where high temperature resistance is required, the low melting polyesters are not completely satisfactory. In some applications, there is a need for rapid and complete fusion of powdered adhesives which have been applied to woven or nonwoven fabrics. The adhesives should fuse readily at temperatures in the range of 130.degree.-150.degree. C. and then solidify to provide a non-tacky, non-dusting adhesive coating which can be subsequently bonded or laminated to face fabrics in heated presses or by dielectric bonding techniques. Such laminates may frequently be required to retain good bond strength at elevated temperatures, such as at 80.degree. C.
Also, there are applications in which it would be highly desirable to be able to fuse and to make bonds with polyester adhesives at temperatures substantially lower than 120.degree. C. For example, in laminating fabrics in older stream presses, the temperature may never exceed the 90.degree.-100.degree. C. range.